The present invention relates to a power supply apparatus having an AC-DC converter and, more particularly, to a power supply apparatus for receiving an AC power supply voltage to apply a DC power supply voltage to office automation equipment such as a personal computer main body.
FIG. 4 shows a conventional power supply apparatus of a personal computer.
The conventional power supply apparatus of a personal computer for receiving an AC (alternating current) power supply voltage to apply a DC (direct current) power supply voltage to the personal computer main body comprises a transformer 11, an AC-DC converter 12, a power supply controller 15, and a push switch 13. The transformer 11 transforms the AC power supply voltage which is applied from input terminals 16a and 16b to a primary coil 11a and outputs the transformed voltage from a secondary coil 11b. The AC-DC converter 12 converts the AC power supply voltage applied from the secondary coil 11b of the transformer 11 into a DC power supply voltage. The power supply controller 15 performs control for applying the DC power supply voltage applied from the AC-DC converter 12 to a personal computer main body 18 through output terminals 17a and 17b. The push switch 13 outputs a control signal to the power supply controller 15 to perform an ON/OFF operation of the DC power supply voltage which is applied from the power supply controller 15 to the personal computer main body 18.
With this arrangement, the power supply apparatus of the personal computer operates as follows.
A commercial AC power supply voltage of 100 V is input from the input terminals 16a and 16b to the primary coil 11a of the transformer 11. At this time, an AC power supply voltage corresponding to the turn ratio of the primary coil 11a to the secondary coil 11b is generated in the secondary coil 11b and output. The AC-DC converter 12 converts the AC power supply voltage applied from the secondary coil 11b of the transformer 11 into a DC power supply voltage. The DC power supply voltage converted by the AC-DC converter 12 is input to the power supply controller 15. Upon reception of a control signal which is output when the push switch 13 is depressed and grounded, the DC power supply voltage received by the power supply controller 15 is applied to the personal computer main body 18 through the output terminals 17a and 17b. The power supply controller 15 continues to apply the DC power supply voltage until the restored push switch 13 is depressed again. When the push switch 13 is depressed again, application of the DC power supply voltage to the personal computer main body 18 is immediately stopped.
In the conventional power supply apparatus of the personal computer as described above, no switching circuit is provided to the primary coil 11a of the transformer 11. Therefore, even when no DC power supply voltage is applied to the personal computer main body 18, some power supply voltage is applied to the AC-DC converter 12 and the power supply controller 15. For this reason, the AC-DC converter 12 and the power supply controller 15 waste the power, and heat and a fault wave are also generated.